The present invention relates to an input device for a computer system. More specifically, the present invention relates to an input device for providing position information to the computer system based on movement of the input device.
A traditional computer input device, such as a mouse, includes a housing, with a ball mounted in the housing. The ball is either configured in a traditional manner in which, in the normal work position, the ball engages a work surface and rotates based on the user's movement of the mouse across the work surface. The ball may also be provided as a track ball, which is rotated by digital manipulation from the user. In either case, position encoders are used to detect rotation of the ball in the mouse, and to provide position information indicative of that rotation to the computer. In many instances, the position information is used to control movement of a visual image (such as a mouse cursor) on the display screen of the computer.
Also, in one prior device, a mouse is configured with the track ball arrangement described above. The track ball is preprinted with a predetermined image. A charge coupled device is used to detect the image on the track ball and detect movement of the image. Movement of the predefined image is used to provide position information to the computer.
However, the prior computer mouse which uses the charge coupled device configuration has a number of significant disadvantages. First, the reaction time of charge coupled devices is quite slow. In addition, processing an image signal from a charge coupled device is computationally intensive and takes a relatively large, and expensive processor. Also, charge coupled devices are highly sensitive to saturation. In other words, if the ambient light conditions are variable, charge coupled devices do not perform well. In addition, if an extraneous light source, such as a flashlight, is directed toward the image producing surface, the charge coupled devices can easily become saturated and their performance then quickly degrades.
Further, another prior computer mouse commercially available from Mouse Systems of CA included a mouse with an LED which was used in conjunction with a mouse pad having a predetermined pattern thereon. The pattern was formed by a grid of blue and red lines. The emissions from the LED was reflected off of the mouse pad to a detector which provided an analog output signal. The signal was in the form of a waveshape with peaks corresponding to the different colored grid lines. From this waveform, the lines were counted and interpolated to obtain position information. Such a mouse system requires a special mouse pad with a special pattern implemented thereon.